A monster asteroid, far more massive than the one that drove the dinosaurs to extinction, punched a huge hole in the Earth's crust billions of years ago and triggered global earthquakes that sent waves of towering tsunamis across all the world's oceans.

Stanford scientists studying ancient rocks in a region of East Africa known as the Barberton Greenstone have for the first time modeled the asteroid's impact and concluded that it must have been one of the most powerful events to ever shape the face of Earth.

The jumbled rocks there hold clear evidence of the stuff thrown up by the asteroid's impact roughly 3.26 billion years ago, but no one has found just where the crater-forming asteroid actually hit, said Stanford geologist Donald Lowe, who has explored the jumbled rocks of the Barberton area for more than a decade.

"There's widespread evidence that the asteroid's impact caused the ground to fail from earthquakes everywhere around the world," said Norman H. Sleep, the Stanford astrophysicist who modeled the event.

"The sky would be red hot from vaporized rocks thrown into the air, everything on the ground would be incinerated, and the oceans would become steam that rained back on Earth for at least a year."

Scientists have long held that after the Earth formed some 4.7 billion years ago, asteroids bombarded the planet for at least 250 million years.

During his years exploring the Barberton area, Lowe said he has found evidence of at least eight of those bombardments, and each is marked by the presence of the rare element iridium that is abundant in asteroids but extremely rare on Earth.

Iridium layers in the Barberton rocks are convincing evidence that they were ejected from the crater that was gouged out by the giant asteroid's impact, Lowe said.

A similar iridium layer was discovered by UC Berkeley geologist Walter Alvarez more than 30 years ago, and helped confirm his theory that an asteroid impact killed off the dinosaurs 65 million years ago - a period much more recent than the estimated age of the Barberton rocks.

Calculating the impact from this monster asteroid, the Stanford scientists estimated that it must have been somewhere between 23 and 36 miles across, and was speeding at 12 miles per second when it hit the Earth. The impact crater must have been at least 300 miles across, Sleep estimated.

Lowe has long specialized in studying the Barberton Greenstone rocks. He first explored the area in 1976, he said, and has worked there almost every year since. It is located near the small town of Barberton, near Swaziland and the South African border with neighboring Mozambique.

"It's a wonderful place for hiking," he said, "with small mountains to climb and rocks of all kinds to study."

Sleep, who specializes in the physics of the forces involved in plate tectonics and the formation of planets, has never been to the Barberton formation.

"I'd like to see it someday," he said.

The Stanford scientists will report the details of their modeling study in the next issue of the journal of the American Geophysical Union, called Geochemistry, Geophysics, Geosystems.